I would use actual heat lamps. They work by radiant heat - that is, they will heat an object, not just the air. I was lucky enough to do my top in the summer time in the sun. It makes a big difference. If it is possible, tent the area and add some space heaters (never leave the area unattended of course).

I used 1x2 boards clamped on to the upper section of the bows to align everything. I got the two center bows vertical and parallel, then used ratchet straps to get the front and rear bows where I wanted them. After you get #1 and #4 bows where you want them, clamp the 1x2 onto them.

The rear curtain on your 1916 top does not go straight up from the tack strip. The top of it will be a couple of inches further back than the tack strip.

Not to confuse the issue, but on earlier cars (1911 and 1912 maybe others) the top of the rear curtain should follow the trajectory of the outside metal back of the backseat. It will be 4+" further back than the tack strip.

Use a plumb bob and a ruler or a vertical level and a ruler to get this accurately measured.

What you don't want to do is push it when it's too cold. The material wont be supple and it will not stretch uniformly or enough and you will not be pleased with the results you have to live with. The ideas above with clamping and spacing are great. Don't rush it and don't take any short cuts, you will regret it in the end. If you get tired or short of patience stop for the day. If you have a choice, a warm location that is not in the direct sun is best for you; it's ok to be in the direct sun when you start but it's miserable by the end of the day. If you can get all your pads and straps on and everything spaced correctly in advance, placing the actual material on the rear and top in the sun is fine. I did my tops when the temp was at least 80 outside, but did the work in the garage with the door open. Plenty warm, but not miserable to work in. I placed the panels in the sun and let them warm before placing them on the car. If you don't heat your garage overnight the night before at least bring the material inside overnight, then spread it out in a warm garage so it gets as warm as possible. Once it's on top of the bows let it sit a bit if you're warming it inside, it will be warmer on top of the car than on on the workbench.

If you are not sure if it's warm enough, or the material supple enough, it's not....

Are your bows all set up? Make sure of all your bow spacing before you start! Any error in this part of the setup will throw everything else off.

My suggestion would be to get the bows and straps and spacing as perfect as you can, then place the material the next day. Even if it's still early you've got a number of hours work and you want to be fresh when you place the panels.

A good looking top stands out, but a poor looking one stands out more. Even if you have to wait it is worth it! I cut corners on my first one and learned the lessons the hard way.... You don't want to do that.